Artificial light at night increases breast cancer risk by 10
Circadian disruption may play a role in breast carcinogenesis. Previous studies reported relationships between outdoor light at night (LAN) and the breast cancer risk, but their findings are mixed. There is also a need to examine LAN and breast cancer incidence according to different individual and environmental characteristics to identify subpopulations at greater risk associated with LAN exposure.

Researchers studied residential outdoor LAN estimated from satellite imagery at baseline (1996) in relation to postmenopausal breast cancer incidence over ~16 years of follow-up in 186981 postmenopausal women including 12318 incident postmenopausal breast cancer cases in the NIH-AARP Diet and Health Study.

- They found that when compared to women in the lowest quintile of baseline LAN, those in the highest quintile had a 10% increase in postmenopausal breast cancer risk.
- The association appeared to be stronger for estrogen receptor (ER) positive breast cancer than for ER-negative cancer.
- These findings also suggested that the relationship between LAN and breast cancer risk may differ by individual characteristics, such as smoking, alcohol drinking, sleep duration and BMI, and neighborhood environment.

In conclusion, This study suggests that higher outdoor LAN exposure may be a risk factor for postmenopausal breast cancer.

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